HTML and URL encoding outgoing messages for the vBulletin chatbox, for Qt.

cbencode.cpp

#include <iomanip>
#include <iostream>

#include <QByteArray>
#include <QSet>
#include <QString>
#include <QTextCodec>

static const QSet<QChar> urlSafeCharacters {
	'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',
	'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',
	'-', '_', '.'
};

static QByteArray encodeChatboxOutgoingText(const QString &inputString)
{
	QByteArray ret;
	bool awaitingLowSurrogate = false;
	uint32_t highUnicodeChar = 0;
	QTextEncoder *encode1252 = QTextCodec::codecForName("windows-1252")->makeEncoder(QTextCodec::ConvertInvalidToNull);

	for (const QChar &c : inputString)
	{
		if (awaitingLowSurrogate)
		{
			if (c.isLowSurrogate())
			{
				highUnicodeChar |= (c.unicode() - 0xDC00);
				highUnicodeChar += 0x010000;

				// append the XML character entity (&#1234;)
				// with URL-escaping
				ret.append("%26%23");
				ret.append(QString::number(highUnicodeChar).toUtf8());
				ret.append("%3B");

				// reset the surrogate pair state
				highUnicodeChar = 0;
				awaitingLowSurrogate = false;
			}
			else
			{
				// leading surrogate not followed by trailing surrogate
				// FIXME: handle this error
			}
		}
		else if (c.unicode() == 0x0000)
		{
			// special case to not interfere with Win1252 detection
			// URL-encode &#0;
			ret.append("%26%230%3B");
		}
		else if (urlSafeCharacters.contains(c))
		{
			// include this character verbatim
			ret.append(static_cast<char>(c.unicode()));
		}
		else if (c.isHighSurrogate())
		{
			highUnicodeChar = (c.unicode() - 0xD800) << 10;
			awaitingLowSurrogate = true;
		}
		else if (c.isLowSurrogate())
		{
			// trailing surrogate following something that isn't a leading surrogate
			// FIXME: handle this error
		}
		else
		{
			// try encoding using Windows-1252
			QByteArray as1252 = encode1252->fromUnicode(&c, 1);
			if (as1252.contains('\0'))
			{
				// Unicode BMP char not in Windows-1252
				// -> HTML-escape with URL-escaping
				ret.append("%26%23");
				ret.append(QString::number(c.unicode()).toUtf8());
				ret.append("%3B");
			}
			else
			{
				// Windows-1252; URL-escape it
				for (const char &b : as1252)
				{
					QString escaped = QString::number((static_cast<unsigned int>(b) & 0xFF), 16).toUpper();
					while (escaped.size() < 2)
					{
						escaped.prepend('0');
					}

					ret.append('%');
					ret.append(escaped.toUtf8());
				}
			}
		}
	}

	return ret;
}

int main(void)
{
	QString str = QString::fromUtf8(
		"P\305\231\303\255li\305\241 "
		"\305\276lu\305\245ou\304\215k\303\275 "
		"k\305\257\305\210 "
		"\360\237\220\216 "
		"\303\272p\304\233l "
		"\304\217\303\241belsk\303\251 "
		"\303\263dy. "
		"\360\237\222\251"
	);
#define URL_HTML(num) "%26%23" #num "%3B"
	QByteArray compare =
		"P" URL_HTML(345) "%EDli%9A%20"
		"%9Elu" URL_HTML(357) "ou" URL_HTML(269) "k%FD%20"
		"k" URL_HTML(367) URL_HTML(328) "%20"
		URL_HTML(128014) "%20"
		"%FAp" URL_HTML(283) "l%20"
		URL_HTML(271) "%E1belsk%E9%20"
		"%F3dy.%20"
		URL_HTML(128169)
	;
#undef URL_HTML

	QByteArray returned = encodeChatboxOutgoingText(str);

	int size = (compare.size() < returned.size()) ? compare.size() : returned.size();

	if (compare.size() != returned.size())
	{
		std::cout << "sizes differ (compare " << compare.size() << ", returned " << returned.size() << ")" << std::endl;
	}

	for (int i = 0; i < size; ++i)
	{
		char c = compare.at(i);
		char r = returned.at(i);

		if (c == r)
		{
			continue;
		}

		std::cout << "byte " << std::setw(3) << i << " compare " << std::setw(3) << static_cast<int>(c) << " ";
		if (c >= 0x20 && c <= 0x7E)
		{
			std::cout << "(" << c << ") ";
		}
		else
		{
			std::cout << "    ";
		}
		std::cout << "returned " << std::setw(3) << static_cast<int>(r) << " ";
		if (r >= 0x20 && r <= 0x7E)
		{
			std::cout << "(" << r << ") ";
		}
		else
		{
			std::cout << "    ";
		}
		std::cout << std::endl;
	}

	return 0;
}